//------------------------------------------------------------------------------
// <copyright file="SqlStream.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
// <owner current="true" primary="true">Microsoft</owner>
// <owner current="true" primary="false">Microsoft</owner>
//------------------------------------------------------------------------------
namespace System.Data.SqlClient {

    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Data.Common;
    using System.Diagnostics;
    using System.Globalization;
    using System.IO;
    using System.Runtime.InteropServices;
    using System.Text;
    using System.Xml;
    using System.Reflection;
    using System.Runtime.CompilerServices;

    sealed internal class SqlStream : Stream {
        private SqlDataReader _reader; // reader we will stream off
        private int           _columnOrdinal;
        private long          _bytesCol;
        int                   _bom;
        private byte[]        _bufferedData;
        private bool          _processAllRows;
        private bool          _advanceReader;
        private bool          _readFirstRow = false;
        private bool          _endOfColumn = false;
        
        internal SqlStream(SqlDataReader reader, bool addByteOrderMark, bool processAllRows) :
            this(0, reader, addByteOrderMark, processAllRows, true) {
        }

        internal SqlStream(int columnOrdinal, SqlDataReader reader, bool addByteOrderMark , bool processAllRows, bool advanceReader) {
            _columnOrdinal = columnOrdinal;
            _reader = reader;
            _bom = addByteOrderMark ? 0xfeff : 0;
            _processAllRows = processAllRows;
            _advanceReader = advanceReader;
        }
        
        override public bool CanRead {
            get {
                return true;
            }
        }

        override public bool CanSeek {
            get {
                return false;
            }
        }

        override public bool CanWrite {
            get {
                return false;
            }
        }

        override public long Length {
            get {
              throw ADP.NotSupported();
            }
        }

        override public long Position {
            get {
                throw ADP.NotSupported();
            }
            set {
                throw ADP.NotSupported();
            }
        }

        override protected void Dispose(bool disposing) {
            try {
                if (disposing && _advanceReader && _reader != null && !_reader.IsClosed) {
                    _reader.Close();
                }
                _reader = null;
            }
            finally {
                base.Dispose(disposing);
            }
        }

        override public void Flush() {
            throw ADP.NotSupported();
        }

        override public int Read(byte[] buffer, int offset, int count) {
            int intCount = 0;
            int cBufferedData = 0;
            
            if ((null == _reader)) {  
                throw ADP.StreamClosed(ADP.Read);
            }
            if (null == buffer) {
                throw ADP.ArgumentNull(ADP.ParameterBuffer);
            }
            if ((offset < 0) || (count < 0)) {
                throw ADP.ArgumentOutOfRange(String.Empty, (offset < 0 ? ADP.ParameterOffset : ADP.ParameterCount));
            }
            if (buffer.Length - offset < count) {
                throw ADP.ArgumentOutOfRange(ADP.ParameterCount);
            }
           
            // Need to find out if we should add byte order mark or not. 
            // We need to add this if we are getting ntext xml, not if we are getting binary xml
            // Binary Xml always begins with the bytes 0xDF and 0xFF
            // If we aren't getting these, then we are getting unicode xml
            if (_bom > 0 ) {
                // Read and buffer the first two bytes
                _bufferedData = new byte[2];
                cBufferedData = ReadBytes(_bufferedData, 0, 2);
                // Check to se if we should add the byte order mark
                if ((cBufferedData < 2) || ((_bufferedData[0] == 0xDF) && (_bufferedData[1] == 0xFF))){
                    _bom = 0;
                } 
                while (count > 0) {
                    if (_bom > 0) {
                        buffer[offset] = (byte)_bom;
                        _bom >>= 8;
                        offset++;
                        count--;
                        intCount++;
                    }
                    else {
                        break;
                    }
                }          
            }
           
            if (cBufferedData > 0) {
                while (count > 0) {
                    buffer[offset++] = _bufferedData[0];
                    intCount++;
                    count--;
                    if ((cBufferedData > 1) && (count > 0)) {
                        buffer[offset++] = _bufferedData[1];
                        intCount++;
                        count--;
                        break;
                    }
                }
                _bufferedData = null;
            }

            intCount += ReadBytes(buffer, offset, count);
            
            return intCount;
        }

        private static bool AdvanceToNextRow(SqlDataReader reader) {
            Debug.Assert(reader != null && !reader.IsClosed);

            // this method skips empty result sets
            do {
                if (reader.Read()) {
                    return true;
                }
            } while (reader.NextResult());
            
            // no more rows
            return false;
        }

        private int ReadBytes(byte[] buffer, int offset, int count) {
            bool gotData = true; 
            int intCount = 0;
            int cb = 0;
            
            if (_reader.IsClosed || _endOfColumn) {
                return 0;
            }
            try {
                while (count > 0) {
                    // if I haven't read any bytes, get the next row
                    if (_advanceReader && (0 == _bytesCol)) {
                        gotData = false;

                        if (_readFirstRow && !_processAllRows) {
                            // for XML column, stop processing after the first row
                            // no op here - reader is closed after the end of this loop
                        }
                        else if (AdvanceToNextRow(_reader)) {
                            _readFirstRow = true;

                            if (_reader.IsDBNull(_columnOrdinal)) {
                                // VSTFDEVDIV 479659: handle row with DBNULL as empty data
                                // for XML column, processing is stopped on the next loop since _readFirstRow is true
                                continue;
                            }
                            
                            // the value is not null, read it
                            gotData = true;
                        }
                        // else AdvanceToNextRow has returned false - no more rows or result sets remained, stop processing
                    }

                    if (gotData) {
                        cb = (int) _reader.GetBytesInternal(_columnOrdinal, _bytesCol, buffer, offset, count);

                        if (cb < count) {
                            _bytesCol = 0;
                            gotData = false;
                            if (!_advanceReader) {
                                _endOfColumn = true;
                            }
                        }                        
                        else {
                            Debug.Assert(cb == count);
                            _bytesCol += cb;
                        } 
                    
                        // we are guaranteed that cb is < Int32.Max since we always pass in count which is of type Int32 to
                        // our getbytes interface
                        count -= (int)cb;
                        offset += (int)cb;
                        intCount += (int)cb;
                    }
                    else {
                        break; // no more data available, we are done
                    }
                }
                if (!gotData && _advanceReader) {
                    _reader.Close();    // Need to close the reader if we are done reading
                }
            } 
            catch (Exception e) {
                if (_advanceReader && ADP.IsCatchableExceptionType(e)) {
                    _reader.Close();
                }
                throw;
            }

            return intCount;
        }

        internal XmlReader ToXmlReader() {
            // Dev11 Bug #315513: Exception type breaking change from 4.0 RTM when calling GetChars on null xml
            // We need to wrap all exceptions inside a TargetInvocationException to simulate calling CreateSqlReader via MethodInfo.Invoke
            return SqlTypes.SqlXml.CreateSqlXmlReader(this, closeInput: true, throwTargetInvocationExceptions: true);
        }
        
        override public long Seek(long offset, SeekOrigin origin) {
            throw ADP.NotSupported();
        }

        override public void SetLength(long value) {
            throw ADP.NotSupported();
        }

        override public void Write(byte[] buffer, int offset, int count) {
            throw ADP.NotSupported();
        }
    }


    // XmlTextReader does not read all the bytes off the network buffers, so we have to cache it here in the random access
    // case. This causes double buffering and is a perf hit, but this is not the high perf way for accessing this type of data.
    // In the case of sequential access, we do not have to do any buffering since the XmlTextReader we return can become 
    // invalid as soon as we move off the current column.
    sealed internal class SqlCachedStream : Stream {
        int          _currentPosition;   // Position within the current array byte
        int          _currentArrayIndex; // Index into the _cachedBytes ArrayList
        List<byte[]> _cachedBytes;
        long         _totalLength;
        
        // Reads off from the network buffer and caches bytes. Only reads one column value in the current row.
        internal SqlCachedStream(SqlCachedBuffer sqlBuf ) {
            _cachedBytes = sqlBuf.CachedBytes;
        }
    
        override public bool CanRead {
            get {
                return true;
            }
        }

        override public bool CanSeek {
            get {
                return true;
            }
        }

        override public bool CanWrite {
            get {
                return false;
            }
        }

        override public long Length {
            get {
                return TotalLength;
            }
        }

        override public long Position {
            get {
                long  pos = 0;
                if (_currentArrayIndex > 0) {
                    for (int ii = 0 ; ii < _currentArrayIndex ; ii++) {
                        pos += _cachedBytes[ii].Length;
                    }
                }
                pos += _currentPosition;
                return pos;
            }
            set {
                if (null == _cachedBytes) {
                    throw ADP.StreamClosed(ADP.ParameterSetPosition);
                }
                SetInternalPosition(value, ADP.ParameterSetPosition);
            }
        }

        override protected void Dispose(bool disposing) {
            try {
                if (disposing && _cachedBytes != null)
                    _cachedBytes.Clear();
                _cachedBytes = null;
                _currentPosition = 0;
                _currentArrayIndex = 0;
                _totalLength = 0;
            }
            finally {
                base.Dispose(disposing);
            }
        }

        override public void Flush() {
            throw ADP.NotSupported();
        }

        override public int Read(byte[] buffer, int offset, int count) {
            int cb;
            int intCount = 0;
            
            if (null == _cachedBytes) {
                throw ADP.StreamClosed(ADP.Read);
            }
            
            if (null == buffer) {
                throw ADP.ArgumentNull(ADP.ParameterBuffer);
            }
            
            if ((offset < 0) || (count < 0)) {
                throw ADP.ArgumentOutOfRange(String.Empty, (offset < 0 ? ADP.ParameterOffset : ADP.ParameterCount));
            }
            
            if (buffer.Length - offset < count) {
                throw ADP.ArgumentOutOfRange(ADP.ParameterCount);
            }
            
            if (_cachedBytes.Count <= _currentArrayIndex) {
                return 0;       // Everything is read!
            }
            
            while (count > 0) {
                if (_cachedBytes[_currentArrayIndex].Length <= _currentPosition) {
                    _currentArrayIndex++;       // We are done reading this chunk, go to next
                    if (_cachedBytes.Count > _currentArrayIndex) {
                        _currentPosition = 0;
                    }
                    else {
                        break;
                    }
                }
                cb = _cachedBytes[_currentArrayIndex].Length - _currentPosition;
                if (cb > count)
                    cb = count;
                Array.Copy(_cachedBytes[_currentArrayIndex], _currentPosition, buffer, offset, cb);

                _currentPosition += cb;
                count -= (int)cb;
                offset += (int)cb;
                intCount += (int)cb;
            }

            return intCount;
        }

        override public long Seek(long offset, SeekOrigin origin) {
            long pos = 0;

            if (null == _cachedBytes) {
                throw ADP.StreamClosed(ADP.Read);
            }
            
            switch(origin)  {
                case SeekOrigin.Begin:
                    SetInternalPosition(offset, ADP.ParameterOffset);
                    break;
					
                case SeekOrigin.Current:
                    pos  =  offset + Position;
                    SetInternalPosition(pos, ADP.ParameterOffset);                    
                    break;
					
                case SeekOrigin.End:
                    pos  = TotalLength + offset;
                    SetInternalPosition(pos, ADP.ParameterOffset);                    
                    break;
					
                default:
                    throw ADP.InvalidSeekOrigin(ADP.ParameterOffset);
            }
            return pos;
        }

        override public void SetLength(long value) {
            throw ADP.NotSupported();
        }

        override public void Write(byte[] buffer, int offset, int count) {
            throw ADP.NotSupported();
        }
        
        private void SetInternalPosition(long lPos, string argumentName) {
            long  pos = lPos;

            if  (pos < 0) {
                throw new ArgumentOutOfRangeException(argumentName);
            }
            for (int ii = 0 ; ii < _cachedBytes.Count ; ii++) {
                if (pos > _cachedBytes[ii].Length) {
                    pos -= _cachedBytes[ii].Length;
                }
                else {
                    _currentArrayIndex = ii;
                    _currentPosition = (int)pos;
                    return;
                }
            }
            if (pos > 0)
                throw new ArgumentOutOfRangeException(argumentName);
        }

        private long TotalLength {
            get {
                if ((_totalLength == 0) && (_cachedBytes != null)) {
                    long pos = 0;
                    for (int ii = 0 ; ii < _cachedBytes.Count ; ii++) {
                        pos += _cachedBytes[ii].Length;
                    }
                    _totalLength = pos;
                }
                return _totalLength;
            }
        }
    }

    sealed internal class SqlStreamingXml {

        int           _columnOrdinal;
        SqlDataReader _reader;
        XmlReader     _xmlReader;
        XmlWriter     _xmlWriter;
        StringWriter  _strWriter;
        long          _charsRemoved;        

        public SqlStreamingXml(int i, SqlDataReader reader) {
            _columnOrdinal = i;
            _reader = reader;
        }

        public void Close() {
            ((IDisposable)_xmlWriter).Dispose();
            ((IDisposable)_xmlReader).Dispose();
            _reader = null;
            _xmlReader = null;
            _xmlWriter = null;
            _strWriter = null;
        }

        public int ColumnOrdinal {
            get {
                return _columnOrdinal;
            }
        }
        
        public long GetChars(long dataIndex, char[] buffer, int bufferIndex, int length) {
            if (_xmlReader == null) {
                SqlStream sqlStream = new SqlStream( _columnOrdinal, _reader, true /* addByteOrderMark */, false /* processAllRows*/, false /*advanceReader*/);
                _xmlReader = sqlStream.ToXmlReader();
                _strWriter = new StringWriter((System.IFormatProvider)null);
                XmlWriterSettings writerSettings = new XmlWriterSettings();
    		    writerSettings.CloseOutput = true;		// close the memory stream when done
		        writerSettings.ConformanceLevel = ConformanceLevel.Fragment;
		        _xmlWriter = XmlWriter.Create(_strWriter, writerSettings);				
            }

            int charsToSkip = 0;
            int cnt = 0;
            if (dataIndex < _charsRemoved) {
                throw ADP.NonSeqByteAccess(dataIndex, _charsRemoved, ADP.GetChars);
            }
            else if (dataIndex > _charsRemoved) {
                charsToSkip = (int)(dataIndex - _charsRemoved);
            }

            // If buffer parameter is null, we have to return -1 since there is no way for us to know the
            // total size up front without reading and converting the XML.
            if (buffer == null) {
                return (long)(-1);
            }
                
            StringBuilder strBldr = _strWriter.GetStringBuilder();
            while (!_xmlReader.EOF) {
                if (strBldr.Length >= (length+ charsToSkip)) {
                    break;
                }
                // Can't call _xmlWriter.WriteNode here, since it reads all of the data in before returning the first char.
                // Do own implementation of WriteNode instead that reads just enough data to return the required number of chars
                //_xmlWriter.WriteNode(_xmlReader, true);
                //  _xmlWriter.Flush();
                WriteXmlElement();
                if (charsToSkip > 0) {
                    // Aggressively remove the characters we want to skip to avoid growing StringBuilder size too much
                    cnt = strBldr.Length < charsToSkip ? strBldr.Length : charsToSkip;
                    strBldr.Remove(0, cnt);
                    charsToSkip -= cnt;
                    _charsRemoved +=(long)cnt;
                }
            }
            
            if (charsToSkip > 0) {
                cnt = strBldr.Length < charsToSkip ? strBldr.Length : charsToSkip;
                strBldr.Remove(0, cnt);
                charsToSkip -= cnt;
                _charsRemoved +=(long)cnt;
            }
            
            if (strBldr.Length == 0) {                    
                return 0;
            }
            // At this point charsToSkip must be 0
            Debug.Assert(charsToSkip == 0);
            
            cnt = strBldr.Length < length ? strBldr.Length : length;
            for (int i = 0 ; i < cnt ; i++) {
                buffer[bufferIndex + i] = strBldr[i];
            }
            // Remove the characters we have already returned
            strBldr.Remove(0, cnt);
            _charsRemoved += (long)cnt;
            return (long)cnt;
        }

        // This method duplicates the work of XmlWriter.WriteNode except that it reads one element at a time 
        // instead of reading the entire node like XmlWriter.
        private void WriteXmlElement() {

            if (_xmlReader.EOF)
                return;
                
            bool canReadChunk = _xmlReader.CanReadValueChunk;
            char[] writeNodeBuffer = null;

            // Constants
            const int WriteNodeBufferSize = 1024;

            _xmlReader.Read();
            switch (_xmlReader.NodeType) {
                case XmlNodeType.Element:
                    _xmlWriter.WriteStartElement(_xmlReader.Prefix, _xmlReader.LocalName, _xmlReader.NamespaceURI);
                    _xmlWriter.WriteAttributes(_xmlReader, true);
                    if (_xmlReader.IsEmptyElement) {
                        _xmlWriter.WriteEndElement();
                        break;
                    }
                    break;
                case XmlNodeType.Text:
                    if (canReadChunk) {
                        if (writeNodeBuffer == null) {
                            writeNodeBuffer = new char[WriteNodeBufferSize];
                        }
                        int read;
                        while ((read = _xmlReader.ReadValueChunk(writeNodeBuffer, 0, WriteNodeBufferSize)) > 0) {
                            _xmlWriter.WriteChars(writeNodeBuffer, 0, read);
                        }
                    }
                    else {
                        _xmlWriter.WriteString(_xmlReader.Value);
                    }
                    break;
                case XmlNodeType.Whitespace:
                case XmlNodeType.SignificantWhitespace:
                    _xmlWriter.WriteWhitespace(_xmlReader.Value);
                    break;
                case XmlNodeType.CDATA:
                    _xmlWriter.WriteCData(_xmlReader.Value);
                    break;
                case XmlNodeType.EntityReference:
                    _xmlWriter.WriteEntityRef(_xmlReader.Name);
                    break;
                case XmlNodeType.XmlDeclaration:
                case XmlNodeType.ProcessingInstruction:
                    _xmlWriter.WriteProcessingInstruction(_xmlReader.Name, _xmlReader.Value);
                    break;
                case XmlNodeType.DocumentType:
                    _xmlWriter.WriteDocType(_xmlReader.Name, _xmlReader.GetAttribute("PUBLIC"), _xmlReader.GetAttribute("SYSTEM"), _xmlReader.Value);
                    break;
                 case XmlNodeType.Comment:
                    _xmlWriter.WriteComment(_xmlReader.Value);
                    break;
                case XmlNodeType.EndElement:
                    _xmlWriter.WriteFullEndElement();
                    break;
            }
            _xmlWriter.Flush();              
        }        
    }   
}
